Au(111)电极表面溴离子吸附诱导的表面应力的理论研究

以Br~-为例,应用格子气模型,建立了阴离子吸附层对Au(111)电极表面应力贡献的统计热力学理论,计算了吸附层Br~-间的相互作用能及表面应力的贡献.计算结果表明,总的表面应力是压缩性的;在高覆盖度区域,表面应力与覆盖度近似呈直线关系;在表面吸附层应力的多种物理起源中,通过底物的分子间作用力有着决定性的贡献,揭示了分子的吸附能间接地起着重要作用.     

蒙脱土/聚苯乙烯复合材料的热分解成炭行为

将聚苯乙烯(PS)树脂与不同种类蒙脱土(MMT)进行熔融复合制备MMT/PS复合材料, 通过X射线衍射(XRD)和高分辨透射电镜(HRTEM)对复合材料的微观结构进行了研究。采用SEM、 EDX、 XRD、 氧指数法和锥形量热法研究了复合材料的热分解成炭行为和燃烧性能。结果表明: 用蒙脱土原土(NaMMT)制备的NaMMT/PS复合材料是一种简单物理混合物, 用有机蒙脱土(OMMT)制备的OMMT/PS复合材料是一种插层-部分剥离型纳米复合材料。MMT与PS质量比为6:100时, OMMT/PS复合材料的热释放速率峰值和平均值分别只有NaMMT/PS复合材料相应值的70.7%和67.4%, 火灾性能指数(FPI)是后者的1.2倍, 氧指数比后者增加1.0%, 热分解残余物表面碳元素含量是后者的2.5倍。OMMT/PS复合材料热分解后在材料表面生成一层厚厚的致密、 连续的含碳硅酸盐残余物层, 起到良好的阻燃作用, 而NaMMT/PS复合材料几乎没有成炭能力, 其热分解产物全部来自NaMMT本身的热分解, 阻燃性能很差。     

二维有机分子吸附层对过渡金属硫化物纳米薄片超低波拉曼光谱的影响

在二维材料下表面与衬底之间的受限空间中,物理吸附物如水分子和有机分子等可形成二维吸附层.然而,这类吸附层如何影响其上层二维材料的性能尚未被探究.本文中,我们结合原子力显微镜、开尔文力显微镜以及超低波拉曼光谱仪来探究有机分子吸附层对其上的少层二硫化钼及二硒化钨纳米薄片性质的影响.随吸附层厚度增加,纳米薄片的超低波呼吸模式...     

亲水基团对十二烷基阴离子乳化剂在SiO2表面吸附影响的分子动力学模拟与试验研究

乳化沥青破乳过程中，乳化剂分子亲水基团吸附于集料表面，亲油基团牵引沥青微滴向集料表面聚集，从而达到破乳。因此，为了探究乳化剂亲水基团对乳化沥青破乳过程的影响，通过分子动力学模拟和电导率试验探究了疏水基团为十二烷基碳链、亲水基团不同的5种阴离子乳化剂在玄武岩主要化学成分（SiO₂）表面的吸附情况。模拟结果表明，亲水基团中的K⁺比Na⁺更能增强十二烷基阴离子乳化剂与水分子间的范德华相互作用，促进十二烷基阴离子乳化剂在SiO₂表面的聚集和吸附；在亲水基团中引入苯基官能团可提高十二烷基阴离子乳化剂与水分子间的范德华相互作用、十二烷基阴离子乳化剂在SiO₂表面的吸附能力，苯基官能团的引入率越高，十二烷基阴离子乳化剂与水分子间的范德华相互作用及十二烷基阴离子乳化剂在SiO₂表面的吸附能力越强；由于库仑力的作用，5种十二烷基阴离子乳化剂的疏水基团尾端C原子、亲水基团极性头S原子在SiO₂表面的扩散行为比十二烷基阴离子乳化剂自身在SiO_2<...     

纳米碳酸钙浓缩浆对环氧涂层耐蚀性的影响

在分散稳定的纳米碳酸钙浓缩浆中,Sa10超分散剂牢固吸附在纳米碳酸钙表面并形成吸附层。纳米碳酸钙浓缩浆提高了环氧涂层的附着力和耐腐蚀性。吸附层的空间位阻效应阻碍纳米碳酸钙粒子间的聚集,且溶剂化层使纳米碳酸钙从极性向非极性转变,提高其与环氧树脂的相容性,保障其在环氧涂料中均匀性和稳定分散。因此,纳米碳酸钙浓缩浆增强了涂层的物理屏蔽作用,使涂层的耐蚀性提高。     

高强高韧聚乙烯醇导电水凝胶的结构与传感性能

为了制备高强高韧导电水凝胶,采用能与聚乙烯醇(PVA)形成氢键相互作用的单宁酸(TA)为物理交联剂,以丙三醇和水为共溶剂制备得到具有纳米纤维网络结构的PVA/TA有机水凝胶;通过浸泡1 mol/L硝酸银溶液得到金属络合作用和氢键作用协同增强增韧的导电水凝胶。研究结果表明,当PVA和TA质量比为2:3时,水凝胶中TA与银离子能形成强烈的络合作用,进一步增强了TA与PVA分子链间形成的物理交联网络,凝胶内部形成了更为致密的网络结构,从而赋予导电水凝胶优异的力学性能,其强度、模量和韧性相较于未引入TA的PVA水凝胶分别提高了4.5倍、5倍和5倍。该导电水凝胶用于应变传感时,表现出优异的灵敏性(GF=99.4)、极高的线性度(R²> 0.99)和良好的循环稳定性(>500圈)。     

水蒸汽辅助凝胶转化法合成连续致密的TAPO-5分子筛膜

采用水蒸汽辅助凝胶转化法合成TAPO-5分子筛膜, 使用XRD、SEM和UV-Vis对膜层进行了表征, 并与传统水热晶化法进行了对比。通过探讨老化模式和晶化时间对TAPO-5分子筛膜表面形貌、晶粒结构与交联性以及膜层覆盖度与致密性的影响, 发现使用水蒸汽辅助凝胶转化法, 在预先老化条件下晶化48 h, 有利于TAPO-5分子筛在载体表面的生长, 在多孔α-Al₂O₃载体表面形成完整、致密的TAPO-5分子筛膜, 也有利于形成骨架钛。     

铝柱撑蒙脱石的制备及其在卷烟产品中的应用

为了解决卷烟烟气有害成分选择性去除的问题,制备氧化铝柱撑蒙脱石及其中间产物羟基铝柱撑蒙脱石材料;采用X射线衍射、扫描电子显微镜、N2物理吸附测试、氨气测试酸性点位分析、微分热重和卷烟添加实验等方法对材料进行表征。结果表明:铝柱撑蒙脱石的(001)晶面的层间距增大,其孔隙以狭缝孔为主;颗粒粒径主要集中在10μm左右;材料表面具有大量的酸性点位;铝柱撑蒙脱石加入卷烟后能不同程度地减小卷烟烟气中苯酚、巴豆醛、氰化氢和氨的质量,羟基铝柱撑蒙脱石的加入还会使烟气中水分的质量分数增大45%,可以作为一种优良的兼具有保水性和吸附性的滤嘴烟气吸附材料。     

水化硅酸钙层间水吸附规律及其对分子结构的影响

水化硅酸钙(C-S-H)是水泥水化产物中的主要组成成分,而层间水对C-S-H的物理化学性能有重要影响。利用分子动力学模拟C-S-H对水分子的吸附,得到280～320 K区间多个温度的C-S-H对水分子的吸附等温线。结果表明,不同温度条件下,C-S-H对水分子的最大吸附量变化不明显,而对水分子的吸附能力随温度升高而降低;提出了温度为280～320 K时,C-S-H对水分子的的吸附式。不同层间水覆盖率的C-S-H晶胞的结构特征表明,随着层间含水量的增大,C-S-H结构分层更加明显。达到不同层间水覆盖率时,吸附水在层间的位置不同导致C-S-H体积增大率不同。吸附水使C-S-H体积增大,密度减小,但C-S-H中原有的原子结构更加紧密。     

电场极化增强的AlN薄片的储氢特性

采用基于密度泛函理论(DFT)的第一原理方法,研究了外加电场对单层AlN薄片储氢性能的影响。通过几何优化得到AlN薄片最稳定的吸氢位置为N原子顶位。研究结果表明:在一定范围内,随着外加电场强度的增加,H2分子在AlN薄片上的吸附能逐渐增大,N—H键长越来越小,H—H键长越来越大。态密度分析表明,加上外电场之后,H-1s轨道与N-2p轨道杂化导致N与H间的交互作用增强。说明电场极化使AlN薄片与H2分子结合得更加紧密,大大提高了AlN薄片的储氢稳定性。而一旦撤销外加电场,H2分子又能恢复到在AlN薄片上的物理吸附状态,使得吸放氢可逆。研究还发现在电场作用下,可同时在AlN薄片的上下表面各吸附一层H2分子,储氢容量显著提高。     

Molecular adsorption of Al3+-doped ZnO (002) crystal plane and its effect on electrical properties

In this paper, the adsorption behavior of molecules in air (O₂ molecules, N₂ molecules, and H₂O molecules) on Al³⁺-doped ZnO (Al–ZnO) (002) crystal plane and its effect on electrical properties of crystal plane have been studied by density-functional theory. The results show that O₂ molecules and H₂O molecules are chemically adsorbed on the crystal planes to form characteristic adsorption species (CAS). N₂ molecules are adsorbed in physical form. The adsorption of three kinds of molecules leads to the decrease of crystal plane conductivity, respectively. The simulation results of conductivity are consistent with the electrochemical impedance spectroscopy fitting data. The optimized adsorption model shows that under the influence of molecules, the surface atoms of the crystal plane undergo restructuring. Partial density of state simulation data show that the electronic orbitals of Al³⁺ and Zn²⁺ on the crystal planes changed obviously after molecular adsorption. The p orbitals of O₂ and H₂O molecules overlap with the d orbital coverage of Zn, respectively. The former has a strong action to form a bond, while the latter has a weak action. The introduction of Al³⁺ changes the electrical and molecular adsorption properties of crystal plane and plays an important role in the regulation of crystal plane function. This shows that the electrical properties of the materials can be controlled by crystal plane ion doping in order to realize the selective adsorption and recognition detection of different molecules.

     

Vacancy‐Driven Gelation Using Defect‐Rich Nanoassemblies of 2D Transition Metal Dichalcogenides and Polymeric Binder for Biomedical Applications

A new approach of vacancy‐driven gelation to obtain chemically crosslinked hydrogels from defect‐rich 2D molybdenum disulfide (MoS₂) nanoassemblies and polymeric binder is reported. This approach utilizes the planar and edge atomic defects available on the surface of the 2D MoS₂ nanoassemblies to form mechanically resilient and elastomeric nanocomposite hydrogels. The atomic defects present on the lattice plane of 2D MoS₂ nanoassemblies are due to atomic vacancies and can act as an active center for vacancy‐driven gelation with a thiol‐activated terminal such as four‐arm poly(ethylene glycol)–thiol (PEG‐SH) via chemisorption. By modulating the number of vacancies on the 2D MoS₂ nanoassemblies, the physical and chemical properties of the hydrogel network can be controlled. This vacancy‐driven gelation process does not require external stimuli such as UV exposure, chemical initiator, or thermal agitation for crosslinking and thus provides a nontoxic and facile approach to encapsulate cells and proteins. 2D MoS₂ nanoassemblies are cytocompatible, and encapsulated cells in the nanocomposite hydrogels show high viability. Overall, the nanoengineered hydrogel obtained from vacancy‐driven gelation is mechanically resilient and can be used for a range of biomedical applications including tissue engineering, regenerative medicine, and cell and therapeutic delivery.     

X-ray-diffraction characterization of Pt(111) surface nanopatterning induced by C60 adsorption

Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task. Theoretical predictions are difficult because of the large number of atoms that have to be considered in the calculations, and experiments aiming to solve the molecule-substrate interaction geometry are almost impossible with standard laboratory techniques. Here, we show that the adsorption of complex organic molecules can induce perfectly ordered nanostructuring of metal surfaces. We use surface X-ray diffraction to investigate in detail the bonding geometry of C(60) with the Pt(111) surface, and to elucidate the interaction mechanism leading to the restructuring of the Pt(111) surface. The chemical interaction between one monolayer of C(60) molecules and the clean Pt(111) surface results in the formation of an ordered sqrt[13] x sqrt[13]R13.9 degrees reconstruction based on the creation of a surface vacancy lattice. The C(60) molecules are located on top of the vacancies, and 12 covalent bonds are formed between the carbon atoms and the 6 platinum surface atoms around the vacancies. In-plane displacements induced on the platinum substrate are of the order of a few picometres in the top layer, and are undetectable in the deeper layers.     

A new method for preparing hydrophilic-activated carbon through ester hydrolysis in an alkaline environment

Hydrophilic-activated carbon was prepared by ester hydrolysis reactions, and was characterized by surface area analysis, Fourier transform infrared spectroscopy, scanning electron microscopy energy dispersive X-ray spectroscopy, and X-ray diffraction. Hydrophilic groups that were introduced on activated carbon surface through ethyl acetate hydrolysis in an alkaline environment were more efficient than those introduced with sodium acetate. During adsorption, the hydrophilic groups on modified activated carbon surface bound with water molecules through H-bonding and increased the adsorption capacity of water vapor. The adsorption isotherms of water vapor were well fitted by the Do model. Water molecules generated larger water clusters around the functional groups at 303 and 313 K. In addition, water desorption from the samples was analyzed by thermogravimetry. Water molecules that were hydrogen-bonded to functional groups exhibited higher thermal stability than those adsorbed in the micropore of activated carbon. Besides, the process of sodium acetate formation on the surface of modified activated carbon was discussed.     

Effect of carboxylic and hydroxycarboxylic acids on cement hydration: experimental and molecular modeling study

Most concrete produced includes chemical admixtures such as air entrainers, set modifiers, water reducers, etc., many of which include organic molecules. Hydroxycarboxylic acids, in particular, retard portland cement hydration. The interaction of such acids with hydrating cement phases is a complex, multi-parameter problem. To elucidate the interaction of hydroxycarboxylic and carboxylic acid retarders on hydration of cement, a combined experimental and molecular-computational approach was used. Glycolic acid, acetic acid, calcium glycolate and calcium acetate were used as model compounds. Molecular dynamics simulations were performed to simulate the interactions of select test compounds with the (001) surface of the portlandite crystal (calcium hydroxide) and the (040) surface of the tricalcium silicate crystal. Hydrogen bond density profiles and binding energies were evaluated. The adsorption isotherm for chelate complexes was determined experimentally by equilibrating aqueous solutions of the agents in the presence of various amounts of solid-phase calcium hydroxide. Finally, isothermal calorimetry experiments were used to quantify effects on hydration rate. The glycolic acid shows significant cement retardation, whereas acetic acid does not retard. Glycolic acid was found to retard hydration via calcium chelation and surface adsorption that involves the adsorption of the calcium chelate complex preferentially on tricalcium silicate. Simulation results reveal that calcium glycolate forms a strong hydrogen bonding network near to calcium hydroxide and hydrated tricalcium silicate surfaces and are responsible for its strong adsorption on these surfaces. While acetic acid forms a strong calcium chelate, it does not associate with calcium hydroxide or unhydrated or hydrated tricalcium silicate surfaces.     

Enantiomeric interactions between nucleic acid bases and amino acids on solid surfaces

Molecular interaction between nucleic acid bases and amino acids is a fundamental process in biology. The adsorption of the molecules on surfaces provides the opportunity to study such interactions in great detail by exploiting the high-resolution imaging capabilities of scanning tunnelling microscopy (STM). The chemisorption of prochiral molecules, such as adenine, on a metal surface causes the adsorbed species to become chiral. Subsequent interactions with inherently chiral molecules may then lead to the formation of diastereoisomers, if the enantiomeric interaction process is sufficiently strong. In the case of adenine adsorption on Cu[110], the chiral adsorbates form homochiral chains. Here, we show that the adenine chain direction is fully correlated with the chirality, and that the alpha-amino acid, phenylglycine, shows a strong chiral preference in its interaction with these chains. STM images clearly demonstrate that S-phenylglycine (R-phenylglycine) binds only to chains rotated 19.5 degrees (anti-) clockwise from the [001] direction. Closer examination reveals that the enantiomeric interaction involves double rows of phenylglycine molecules and the adenine chains. This is the first observation at the molecular level of diastereoisomeric interaction, and demonstrates that STM is a powerful method for studying the details of these interactions.     

Nucleation of supercooled water on solid surfaces

Heterogeneous nucleation of water was investigated using molecular dynamics simulation. Solid with fcc (111) surface was placed at the bottom of a cell consisting of 864 water molecules. ST2 model with NPT ensemble was used. The pressure and temperature were set to be 0.1 MPa and 275 K, respectively. The interaction between water and the solid was based on the equations proposed by Spohr. Exception was made on the lattice constant which was slightly modified to fit with that for ice structure. The shape of the solid surface was considered. It was found that the only one layer of water molecules was adsorbed in a case of a flat surface, whereas ice nucleation occurred by removing some of the atoms from the surface. Spohr's interaction was also modified so that the dipole moment of water became anti-ferroelectric. It was found that the modification increased the ice growth, further. The effect of lattice constant of solid on nucleation was also investigated. It was found that the variation on lattice constant with a few percent from that of ice was acceptable for nucleation, especially on shrinking side. On expanding side, however, it gave some gaps for water molecules to fit in other than that for ice structure, and it prevented the growth of ice. Hence, a guideline for the selection of ice nucleus material was obtained.     

Anatase TiO₂ crystal facet growth: mechanistic role of hydrofluoric acid and photoelectrocatalytic activity

This work reports a facile hydrothermal approach to directly grow anatase TiO(2) crystals with exposed {001} facets on titanium foil substrate by controlling pH of HF solution. The mechanistic role of HF for control growth of the crystal facet of anatase TiO(2) crystals has been investigated. The results demonstrate that controlling solution pH controls the extent of surface fluorination of anatase TiO(2), hence the size, shape, morphology, and {001} faceted surface area of TiO(2) crystals. The theoretical calculations reveal that {001} faceted surface fluorination of anatase TiO(2) can merely occur via dissociative adsorption of HF molecules under acidic conditions while the adsorption of Na(+)F(-) is thermodynamically prohibited. This confirms that the presence of molecular form of HF but not F(-) is essential for preservation of exposed {001} facets of anatase TiO(2). Anatase TiO(2) crystals with exposed {001} facets can be directly fabricated on titanium foil by controlling the solution pH ≤ 5.8. When pH is increased to near neutral and beyond (e.g., pH ≥ 6.6), the insufficient concentration of HF ([HF] ≤ 0.04%) dramatically reduces the extent of surface fluorination, leading to the formation of anatase TiO(2) crystals with {101} facets and titanate nanorods/nanosheets. The anatase TiO(2) nanocrystals with exposed {001} facets exhibits a superior photoelectrocatalytic activity toward water oxidation. The findings of this work clarify the mechanistic role of HF for controlling the crystal facet growth, providing a facile means for massive production of desired nanostructures with high reactive facets on solid substrates for other metal oxides.     

高强度疏水缔合水凝胶的重塑性能机理

将丙烯酰胺和少量的疏水单体辛基酚聚氧乙烯(4)醚丙烯酸酯溶解于十二烷基硫酸钠水溶液中,采用胶束共聚的方法成功制备了疏水缔合水凝胶(HA-gels)。HA-gels除具有良好的力学性能以外,还具有重塑性能。为了研究HA-gels的重塑性能,对其应力松弛行为进行了表征。研究结果表明,HA-gels应力松弛过程可以分为四个阶段:第一阶段是交联点间亲水长链的应力松弛过程;第二阶段是交联点间亲水长链已经高度取向;第三阶段是交联网络的结构重排过程;第四阶段是HA-gels的应力完全消除。因此,HA-gels内的交联点在外力的作用下可以解缔合和重新缔合来实现交联网络的结构重组,从而赋予了HA-gels的重塑性能。